Measurement of force with high accuracy and digital output has potential for application in widely varying fields such as pressure measurement, well logging, electronic engine control, oceanography, meteorology, tilt sensors, intrusion detectors, seismology, weighing, accelerometers, and industrial process control.
A widely-used technique for force measurement utilizes a vibrating quartz resonator with frequency of vibration proportional to the force applied. These resonators are capable of high resolution and result in a digital output which make them attractive for use with digital microprocessors. However, existing quartz resonators require precision machining of complex shapes which may be prohibitively expensive to manufacture or which may result in costly, unreliable units.
A desirable property of a vibrating quartz resonator force transducer is to have a high mechanical Q. Q is proportional to the ratio of energy stored to energy lost per cycle in the vibration system. A lower Q means that a larger source of external energy must be supplied to maintain the oscillations and the oscillator will possess a less stable resonant frequency. The present invention generally possesses a higher mechanical Q than that available with existing quartz resonator force transducers.
Some quartz resonator force transducers are exemplified by U.S. Pat. Nos. 3,399,572; 3,470,400; 3,479,536; 3,505,866; 4,020,448; 4,067,241; 4,091,679; 4,104,920, and 4,126,801. As can be seen, these resonators either require complex and therefore expensive crystal shapes or complex and therefore expensive metal parts.